Bose's journey from Germany to Singapore by submarine was a well-remarked incident of World War II history. But what was the need for the Germans or the Italians to use a submarine to transfer a civilian? Was it impossible for them to arrange a flight? Or was it done to force Bose, whose relationship with Hitler was frosty, to make an uncomfortable and unsafe journey?

Even so, airplanes in WW2 were not nearly as safe as they are today. Worse, they can be spotted, and if spotted in range of an enemy air field fairly easily taken down. This is, in fact, how the allies killed Admiral Yamamoto. So it is quite likely submarine transport would have been safer, even if air transport was an option.

In fact, the transfer to the Japanese sub occurred 10 days after Yamamoto was shot down. Its likely both Bose and the Imperial Navy wouldn't be inclined to risk another VIP that way so soon.

trying to envision a route they could have flown, and indeed it runs into trouble over the Black Sea, a long way from Japan. While Turkey and Iran weren't active warzones, they were nominally under allied control as far as Germany was concerned. India of course was British controlled, as was Afghanistan. Even a Condor would be unable to make it from Romania to China nonstop.
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jwentingFeb 14 '13 at 7:36

@jwenting Then how did the diplomatic staff of the Allied powers travel?
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AraniFeb 14 '13 at 13:25

@Arani The allied powers controlled the seas, traveled by ship mainly. They also had access to the small number of very long range flying boats like the Boeing 314 Clippers. And of course they controlled large contiguous landmasses, allowing them the luxury of safe airports at convenient intervals.
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jwentingFeb 14 '13 at 14:25

Wait... wasn't Yamamoto killed as a result of sigint, and not being "spotted"?
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DVKFeb 14 '13 at 22:34

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@DVK - A bit of both. Without the sigint they wouldn't have known where or when to look. But to borrow from Douglas Adams, The Pacific... is big. Really big. You just won't believe how vastly hugely mindbogglingly big it is. Presumably the same sigint would have been just as capable of finding out that the Japanese were transporting Bose, but a submarine would have been much harder to find.
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T.E.D.♦Feb 14 '13 at 23:07

Bose was sent on U180, a specially built fast cargo submarine whose main role was to refuel other U-boats operating in the Indian Ocean, however its cargo also included three tons of Gold for the German Embassy in Tokyo, therefore the handover had several diplomatic aspects.

In fact Abwher parachutists were infiltrated by air into Afghanistan and these men were responsible for collecting Bose from the Khyber pass and leading him to Kabul where there was an airstrip used to repatriate him to Germany via Rhodes.

Some time later there was a flight to China made by the Italian Servizi Aerei Speciali using the SM 75 aircraft, "MM-60539." The original successful flight left via the Crimea at great peril so the second of these flights was proposed via the same airfield in Kabul.

There was no need to infiltrate Bose back into India as he was worth more to the Axis being sent back to Japan via the submarine base at Singapore to influence Indians in Malayan POW camps to desert and join the Axis cause